Apple cider vinegar and lemons are definitely acidic. I think you have to get over your GERD SYMPTOMS before you use these two very beneficial acids (THEY DO LOWER STOMACH ACID, THEY ARE ALKALINE WHEN THEY REACH THE STOMACH) as salad dressings with olive oil, and use them sparingly even then.
Of course, they will burn going down your esophagus especially people that take the apple cider vinegar straight, it's an acid. You should at least dilute it in a glass of water.
It all comes back to ALKALINE, I just wish everyone would just start realizing that it's your only hope to curing your GERD symptoms and get off all these drugs.
If you decrease your stomach acid by not eating acid foods and help yourself with supplements you will eventually heal your esophagus.
Take Aloe Vera (refrigerate after opening) it sooths the esophagus and helps it heal.
Use DGL licorice TABLETS, dissolve in mouth 20 minutes before eating.
It's very strict though and you need alot of self-control.
At least try to not eat the most acidic foods like meat - eat tofu instead, very high in protein - mix it in with some vegetables like string beans, carrots, spinach, red beets, avocado.
I use Quinoa and Millet grains for more protein and mix them into my food.
My friend, who is a medical doctor, eats mostly like this. She is a vegetarian and has always relied on tofu, quinoa and millet as her proteins.
Hope this helps.